The present invention relates generally to seals for rotating shafts, and, more particularly, to a multi-stage, stationary, labyrinth seal assembly surrounding a rotating shaft.
Labyrinth seals have been used to minimize fluid flow from a high pressure side of the seal to a low pressure side thereof. However, there is inevitably some fluid leakage across the labyrinth seal especially when the seal is established along a rotating body, such as a rotating shaft, or the like, since the rotating body often causes a flow of air radially outwardly from the low pressure side of the labyrinth seal, thereby forming a vacuum and increasing the pressure drop across the seal.
In U.S. Pat. No. 5,085,443, an external fluid source is used to limit such leakage. This is accomplished by a plurality of radially extending purge openings formed in the seal to provide a flow of inert gas around the labyrinth seal to provide a thin fluid film through the radial purge openings, so that the seal rides on the thin film. The fluid is introduced at the center of the seal to provide buffering to minimize leakage of lubricating oil or process fluids. However, the external fluid source increases the complexity of the structure and presents a problem if no such external fluid source is readily available.
In U.S. Pat. No. 5,224,713, radial passages are disclosed in a rotating labyrinth seal. The passages extend from the low pressure side of the labyrinth seal to a channel between the teeth of the seal at the low pressure end of the seal. Air entrained in the passages is subjected to centrifugal force causing the air to move away from the center of rotation. The passages function as a pump to move the air radially outwardly. This device however, requires that the labyrinth seal body rotate and is therefore not adaptable to a stationary labyrinth seal body.
Therefore, what is needed is a stationary labyrinth seal assembly which minimizes or eliminates leakage across the seal and which does not require an external fluid source.